PI4ZLB

Not every project has to be complicated– reinventing the wheel has its place, but sometimes you find a module or two that does exactly what you want, and the project is more than halfway done. That the kind of project [mircemk]’s Simple Retro Style VFO is — it’s a variable frequency oscillator for HAM and other use, built with just a couple of modules.

The modules in question are the SI5351 Clock Generator module, which is a handy bit of kit with its own crystal reference and PLL to generate frequencies up to 150 MHz, and the Elecrow CrowPanel 1.28inch-HMI ESP32 Rotary Display. The ESP32 in the CrowPanel controls the SI5351 module via I2C; control is via the rest of the CrowPanel module. This Rotary Display is a circular touchscreen surrounded by a rotary display, so [mircmk] has all the inputs he needs to control the VFO.

To round out the parts count, he adds an appropriate connector, plus a power switch, red LED and a lithium battery. One could include a battery charger module as well, but [mircmk] didn’t have one on hand. Even if he had, that still keeps the parts count well inside the single digits. If you like video, we’ve embedded his about the project below; if not the write up on Hackaday.io is upto [mircmk]’s typical standard. 

People have been using the SI5351 to make VFOs for years now, but the addition of the round display makes for a delightfully retro presentation.

Thanks to [mircmk] for the tip.

If you own a handheld transceiver of any type then the chances are it will come with a “rubber duck” style antenna. These flexible rubber-coated antennas are a compromise in performance, being significantly smaller than a wavelength at their frequency of operation. [OM40ET] has an interesting video in which he investigates this by tearing down a cheap rubber duck antenna and an even cheaper fake.

These antennas usually have a flexible upper section and a bulge at the bottom over the connector. The fake one has nothing in the bulge except the antenna wire and thus has a very high SWR, while the “real” one has a loading coil. This coil is an interesting design, because it’s designed such that the antenna has two resonant points at the 2 metre and 70 centimetre amateur bands. On paper it’s a tapped coil fed at the tap through a capacitor for matching, but a more detailed appraisal will tell you that the two halves of the coil are designed to return those two resonances. It’s still a not-very-good antenna, but the fact that it works at all is something.

If you want something better at VHF and haven’t got much space, all is not lost. We recently featured a VHF magnetic loop.

The magnetic loop antenna is a familiar sight in radio amateur circles as a means to pack a high performance HF antenna into a small space. It takes the form of a large single-turn coil made into a tuned circuit with a variable capacitor, and it provides the benefits of good directionality and narrow bandwidth at the cost of some scary RF voltages and the need for constant retuning. As [VK3YE] shows us though, magnetic loops are not limited to HF — he’s made a compact VHF magnetic loop using a tin can.

It’s a pretty simple design; a section from the can it cut out and made into a C shape, with a small variable capacitor at the gap. The feed comes in at the bottom, with the feed point about 20 % of the way round the loop for matching. The bandwidth is about 100 MHz starting from the bottom of the FM broadcast band, and he shows us it receiving broadcast, Airband, and 2 meter signals. It can be used for transmitting too and we see it on 2 meter WSPR, but we would have to wonder whether the voltages induced by higher power levels might be a little much for that small capacitor.

He’s at pains to point out that there are many better VHF antennas as this one has no gain to speak of, but we can see a place for it. It’s tiny, if you’re prepared to fiddle with the tuning its high Q gets rid of interference, and its strong side null means it can also reduce unwanted signals on the same frequency. We rather like it, and we hope you will too after watching the video below.

Any radio amateur will tell you about the spectre of TVI, of their transmissions being inadvertently demodulated by the smallest of non-linearity in the neighbouring antenna systems, and spewing forth from the speakers of all and sundry. It’s very much a thing that the most unlikely of circuits can function as radio receivers, but… teeth? [Ringway Manchester] investigates tales of musical dental work.

Going through a series of news reports over the decades, including one of Lucille Ball uncovering a hidden Japanese spy transmitter, it’s something all experts who have looked at the issue have concluded there is little evidence for. It was also investigated by Mythbusters. But it’s an alluring tale, so is it entirely fabricated? What we can say is that teeth are sensitive to sound, not in themselves, but because the jaw provides a good path bringing vibrations to the region of the ear. And it’s certainly possible that the active chemical environment surrounding a metal filling in a patient’s mouth could give rise to electrical non-linearities. But could a human body in an ordinary RF environment act as a good enough antenna to provide enough energy for something to happen? We have our doubts.

It’s a perennial story (even in fiction), though, and we’re guessing that proof will come over the coming decades. If the tales of dental music and DJs continue after AM (or Long Wave in Europe) transmissions have been turned off, then it’s likely they’re more in the mind than in the mouth. If not, then we might have missed a radio phenomenon. The video is below the break.

The first transistors were point contact devices, not far from the cats-whiskers of early radio receivers. They were fragile and expensive, and their performance was not very high. The transistor which brought the devices to a mass audience through the 1950s and 1960s was the one which followed, the alloy diffusion type. [Play With Junk] has a failed OC71 PNP alloy diffusion transistor, first introduced in 1957, and has cracked it open for a closer look.

Inside the glass tube is a small wafer of germanium crystal, surrounded by silicone grease. It forms the N-type base of the device, with the collector and emitter being small indium beads fused into the germanium. The junctions were formed by the resulting region of germanium/indium alloy. The outside of the tube is pained black because the device is light-sensitive, indeed a version of this transistor without the paint was sold as the OCP71 phototransistor.

These devices were leaky and noisy, with a low maximum frequency and low gain. But they were reliable and eventually affordable, so some of us even cut our electronic teeth on them.

As you might expect, the University of Puerto Rico at Arecibo has a fascination with radio signals from space. While doing research into the legendary “Wow! Signal” detected back in 1977, they realized that the burst was so strong that a small DIY radio telescope would be able to pick it up using modern software-defined radio (SDR) technology.

This realization gave birth to the Wow@Home project, an effort to document both the hardware and software necessary to pick up a Wow! class signal from your own backyard. The University reasons that if they can get a bunch of volunteers to build and operate these radio telescopes, the resulting data could help identify the source of the Wow! Signal — which they believe could be the result of some rare astrophysical event and not the product of Little Green Men.

Ultimately, this isn’t much different from many of the SDR-based homebrew radio telescopes we’ve covered over the years — get a dish, hook your RTL-SDR up to it, add in the appropriate filters and amplifiers, and point it to the sky. Technically, you’re now a radio astronomer. Congratulations. In this case, you don’t even have to figure out how to motorize your dish, as they recommend just pointing the antenna at a fixed position and let the rotation of the Earth to the work — a similar trick to how the legendary Arecibo Observatory itself worked.

The tricky part is collecting and analyzing what’s coming out of the receiver, and that’s where the team at Arecibo hope to make the most headway with their Wow@Home software. It also sounds like that’s where the work still needs to be done. The goal is to have a finished product in Python that can be deployed on the Raspberry Pi, which as an added bonus will “generate a live preview of the data in the style of the original Ohio State SETI project printouts.” Sounds cool to us.

If you’re interested in lending a hand, the team says they’re open to contributions from the community — specifically from those with experience RFI shielding, software GUIs, and general software development. We love seeing citizen science, so hopefully this project finds the assistance and the community it needs to flourish.

Thanks to [Mark Stevens] for the tip.